A vibration-insulating grommet is widely used in the fields of an automobile, an electronics product and a general industrial machine. Particularly in an automobile field, a vibration-insulating grommet is used broadly as a vibration-insulating material including a mechanism component such as an ABS (antilock brake system), an EBS (electronically controlled brake system or regenerative braking system) and an ESC (electronic stability control or slip prevention device) of a brake control unit, an engine auxiliary unit, and a pipe of a fuel cell vehicle.
The vibration-insulating grommet, which mainly works to reduce vibration transmissibility and control displacement of a support body, is required to work variously dependent on a target for which the vibration transmissibility should be reduced. For example, in case of an ECB of a brake control unit, the required performance is to protect and support a machine against vibration transmitted from a road surface, or reduce vibration transmitted to a vehicle interior when switching a relay switch. Further, in case of a fuel cell vehicle, the required performance is to support stack wiring with vibration-insulating.
As mentioned above, a rubber material used for a vibration-insulating grommet is required to have the following properties.
(1) A high damping property for the purpose of reducing vibration of a target (especially in resonance).
(2) A wide range of hardness variation (i.e., hardness form 10° to 70°) for exerting a vibration-insulating effect in a wide frequency band. Particularly in recent years, it is required to have low hardness for the purpose of reducing a weight of a component unit (e.g., hardness of 60° or less, preferably 50° or less, more preferably 40° or less).
(3) Excellent in kneading, roll-processing and crosslinking performance of a rubber material.
(4) No silicon compound contained for the purpose of avoiding component contamination and defectiveness of electric circuit/relay contact.
Here, a rubber material fulfilling the above properties and applicable to a vibration-insulating grommet includes butyl rubber. Butyl rubber has an excellent damping property over a wide range of frequency bands, and is excellent in shock absorption and energy absorption. Further, butyl rubber has a relatively small degree of unsaturation, leading to excellent in weather resistance, heat resistance and ozone resistance.
Conventionally, a variety of compositions have been studied in order to improve the performance of a vibration-insulating rubber via using butyl rubber as a rubber material. For example, Patent Document 1 discloses a vibration-insulating rubber composition to which silicon oil is added for increasing damping performance and decreasing adhesiveness of butyl based rubber so that the procesability and formability of the vibration-insulating rubber composition are improved.